The present invention relates to frequency estimation for communication systems, and more specifically, to a frequency estimation method and system using a multiple linear regression technique.
In current communication systems, information is transmitted over a channel after modulating to a carrier signal. The carrier is modulated by varying one or more of its parameters, such as amplitude, frequency, or phase, according to the information being transmitted. In the process of transmission, the communication channel alters the characteristics of the transmitted signal and, typically, adds random interference, commonly known as Additive White Gaussian Noise (AWGN). These modifications can make the transmitted signal difficult to recognize at a receiver.
Phase shift keying (PSK) modulation is frequently employed in communication systems, and mobile units may exhibit a significant amount of frequency drift or variation in their local oscillators. Therefore, an important issue during reception is resolution of the frequency inherent in the received signal. The frequency of the received signal typically changes over time due to instability, such that the receiver must continuously estimate phase and frequency to maintain synchronization between the transmitter and receiver.
Training sequences embedded in the received signal are typically used to train or calibrate the receiver before handling actual data. Various techniques have been proposed to determine the frequency of the received signal according to the training sequences. Among these techniques, linear regression is commonly used for frequency estimation, comparing calculation of an angle of each input symbol and a symbol phase difference between a current and a previous symbol. The calculated phase differences are accumulated, and a linear regression analysis is applied to the sum of the phase difference to obtain frequency estimation. The drawback of this frequency estimation method is unreliable performance due to low signal to noise ratio (SNR) increased frequency estimation error when burst error occurs in the pilot signal.